Retrofittable apparatus for converting a substantially planar surface into an electronic data capture device

ABSTRACT

A graphic data-acquisition system which employs an active tracking system provides a retrofittable apparatus for converting a substantially planar surface into an electronic data capture device, in which the components of the system are readily retrofittable, at relatively low cost, to a wide variety of otherwise conventional writing-surface structures, such as so-called dry-erase whiteboards. Conventional triangulation techniques are used to track the position and motion of a writer or eraser. An encoding facility associated with the writing implement provides the ability to distinguish whether the writing implement is used for marking or an as erasing implement, as well as determining the nature or character of written line width or eraser swath. A data stream thus generated can be used in a variety of ways, such as for example, to feed information into the memory of a digital computer, and/or to feed information for transmission to remote stations.

This application is a continuation of U.S. patent application Ser. No.09/443,164, filed Nov. 19, 1999, now U.S. Pat. No. 6,266,051, which is acontinuation of U.S. patent application Ser. No. 08/804,491, filed Feb.21, 1997, now U.S. Pat. No. 6,067,080.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates to electronic data capture devices. Moreparticularly, the invention relates to a retrofittable apparatus forconverting a substantially planar surface into an electronic datacapture device.

2. Description of the Prior Art

Electronic blackboards date at least to the mid-1960s, at which timeemphasis was placed on the communication of graphical data, specificallyhandwriting and sketches, from one location to another. U.S. Pat. No.3,706,850 discloses a system related to such activity.

At about the same time, graphic tablets that allowed the entry of linedrawings into a computer were developed. U.S. Pat. No. 3,838,212 is anearly example of developments in this area.

By the mid-1980s, a third kind of a product group was developed toaddress the need for a local hard copy of material written and sketchedonto a dry-erase, so-called whiteboard. This generic group of systems,known collectively as electronic copyboards (ECBs), relatesfundamentally to stand-alone devices that have much in common with wellknown reducing photocopiers.

Each of these devices attempts to provide the user with a naturalcommunication metaphor that uses familiar writing tools. In the case ofelectronic blackboards and electronic copyboards, the metaphor is afixed wall-mounted surface meant for mass viewing, in which marking orwriting is accomplished by the use of colored markers, and in whicherasing is accomplished by wiping the surface with an eraser. In thecase of the graphic tablet, the metaphor is a desktop slate and stylusmeant for individual use.

Those skilled in the art recognize that both electronic blackboards andelectronic copyboards typically require dedicated, highly specializedsurfaces and equipment structures. These specialized structures resultin an immobile, cumbersome, and relatively expensive system. Systems andapproaches generally in this line of technical art are illustrated, forexample, in U.S. Pat. No. 3,613,066 to Cecreman, U.S. Pat. No. 4,558,313to Garwin et al., U.S. Pat. No. 4,506,354 to Hansen, U.S. Pat. No.4,670,751 to Enokido, U.S. Pat. No. 4,711,977 (U.S. Pat. No. Re. 33,936)to Miyamori, U.S. Pat. No. 4,777,329 to Mallicoat, U.S. Pat. No.4,814,552 to Stefik et al., U.S. Pat. No. 5,248,856 to Mallicoat, U.S.Pat. No. 5,023,408 to Murakami, and U.S. Pat. No. 5,434,370 to Wilson.

The '066 patent discloses a display panel and means responsive to thepositions and moves of a pointer on the panel to generate informationsignals for a computer. Thin, coherent light beams parallel to thesurface of the panel a systematically and repetitively displaced incrossing relation to scan at least part of the surface. The position ofa marker relative to the display panel is detected by interference ofthe marker with the scanned light beams.

The '313 patent focuses on an indicator-to-data processing interfacewhich employs a light source and a background reflector as constituentsin a system to monitor occlusion of light occurring from the positioningand movement of a manually moved indicator over a surface.

The '751 patent discloses an eraser for an electronic blackboard havinga variable erasing area. The eraser includes a small area erasing unitand a detachable large area erasing unit. Detectors determine when theeraser is touched to the surface of the board, as well as whether thesmall area erasing unit or the large area erasing unit are currently inuse.

The '977 patent discloses an electronic blackboard, writing instrument,and position-detecting control unit. The system uses magnetic bias todetect the position of an writing/erasing element relative to that ofvideo information displayed on a writing surface.

The '329 and '856 patents address a graphic input system which employsultrasound (the '329 patent) or scanned light (the '856 patent) tomonitor the position of a mobile element over a surface. The '856 patentincludes at least two spaced transceiver-structure stations thatoptically track the position and motion of a writer or eraser based uponbar code techniques. While it is suggested in the '856 patent that thesetransceiver-structure stations may be retrofitted to a conventionalwriting-surface structure, no discussion is provided for performing suchretrofit, nor is it clear that the scanning technology disclosed wouldbe suitable for a retrofit application, where the spaced, separatestructures cannot be rendered insensitive to in-use relational changes(for example, movement and vibration of the white board occasioned bymovement of the writing implement to and across the surface of the whiteboard during use), and where adequate precision to effect an accuratescan cannot be achieved without regular calibration during use due tothe relative positional instability of the multiple spaced sensors.

The '552 patent discloses an input device, or stylus, for entering handdrawn forms into a computer comprising a writing instrument, a pressureswitch doe determining whether the instrument is in contact with thewriting surface, an acoustic transmitter for triangulating the positionof the stylus on the surface, and a wireless transmitter fortransmitting data and timing information to the computer. In operation,the stylus transmits an infrared signal which the system receivesimmediately, and an ultrasound pulse which two microphones receive aftera delay which is a function of the speed of sound and the distance ofthe stylus from each microphone. From this information the system cancalculate the position of the stylus. Switches for indicating functionsare mounted on the stylus. Multiple styluses can be used, eachtransmitting a distinctive identification code so that the system candetermine which stylus is the signal source.

The '408 patent describes an electronic blackboard, including a sensingtablet which senses the position of a writing tool that includes a tunedcircuit having a predetermined resonant frequency.

The '370 patent discloses a graphic data acquisition system in which adigitized record is produced according to the X, Y, and Z position of awriting implement relative to a writing surface. An expanse ofelectromagnetic radiation is generated in a zone adjacent to the writingsurface, and an electromagnetic interactive pen interacts with suchelectromagnetic radiation to produce a signal that locates the penrelative to the writing surface.

Prior art systems of the type outlined above are relatively complex,immobile, and costly. Typically, they are not readily retrofittable atall, much less to a wide variety of writing-surface structures which arealready in hundreds of thousands of users' possessions. In fact, foruseful and accurate operation, such systems depend upon a specificsurface having either embedded sensors or otherwise preciselypredetermined qualities. Further, prior art systems are not particularlyadapted to yield information about the condition of a writing stylus oran eraser much beyond its position or station over a writing surface.

Accordingly, it would be advantageous to provide a novel graphicdata-acquisition system which offers not only the various features andadvantages made available by prior art, but which further effectivelyaddresses the various performance, cost, simplicity, mobility andsophistication issues mentioned above. It would be especiallyadvantageous to provide such a system that is readily retrofitted toexisting writing surfaces without the need for special mountingarrangements or regular calibration, while providing a high degree ofprecision and stability, and while also providing a rich complement ofsophisticated features.

SUMMARY OF THE INVENTION

The invention is a graphic data-acquisition system which employs acontinuously active tracking system to provide a retrofittable apparatusfor converting a substantially planar surface into an electronic datacapture device. Various techniques are disclosed that allow thefabrication of a retrofittable assembly, such that any substantiallyplanar surface may be converted into an electronic data capture device.Thus, the components of the system are readily retrofittable, atrelatively low cost, to a wide variety of otherwise conventionalwriting-surface structures, such as so-called dry-erase whiteboards.

The invention employs any conventional triangulation technique to trackthe position and motion of a writer or eraser. As discussed above, manysuch techniques are known, but these techniques have traditionallyrequired a specialized or dedicated writing surface or have beenotherwise unsuited for retrofit to an existing writing surface. Theinvention exploits to advantage both the significant improvements inmodern tracking technology and a novel and improved fitting techniquethat allows rapid and efficient retrofit of a tracking assembly to adry-erase whiteboard or other planar surface, while providing aprecision tracking system that accurately tracks a writing implement inthree dimensions, thus capturing all marks placed on the markingsurface.

Further, by using an encoding facility associated with a writingimplement the invention provides the ability to distinguish whether thewriting implement is used for marking or an as erasing implement, aswell as determining the nature or character of written line width oreraser swath, for example specific color in the instance of a coloredwriting instrument. A data stream thus generated can be used in avariety of ways, such as for example, to feed information into thememory of a digital computer, and/or to feed information fortransmission to remote stations for live presentation of writingactivity occurring on the writing-surface area in the system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a retrofittable apparatus forconverting a substantially planar surface into an electronic datacapture device according to the invention;

FIG. 2 is a partially sectioned, side view of a sensor array attachmentmethod according to a first preferred embodiment of the invention;

FIG. 3 is a partially sectioned, side view of a sensor array attachmentmethod according to a second, equally preferred embodiment of theinvention;

FIG. 4 is a partially sectioned, side view of a sensor array attachmentmethod according to a third, equally preferred embodiment of theinvention;

FIG. 5 is a partially sectioned, side view of a sensor array attachmentmethod according to a fourth, equally preferred embodiment of theinvention;

FIG. 6 is a perspective view of an L-shaped sensor array according tothe invention;

FIGS. 7a-7 c show alternative embodiments of the invention that provideside, bottom, and top mounting configurations for fitting a sensor arrayto a writing surface; and

FIG. 8 is a partially sectioned, side view of a marking implementaccording to the invention;

FIGS. 9a-9 c provide an end view (FIG. 9a), a side view (FIG. 9b), and aperspective view (FIG. 9c) of a two-point or Squeegee-type eraseraccording to an alternative embodiment of the invention;

FIG. 10 provides an erasing edge view of a two-point or Squeegee-typeeraser according to the invention;

FIG. 11 shows the use of the eraser of FIGS. 9a-9 c and 10 to erase athin area of a presentation board in a motion that is parallel to the Yaxis of the eraser;

FIG. 12 shows the eraser of FIGS. 9a-9 c and 10 in use to erase a widearea in a motion that is parallel to the X axis of the presentationboard; and

FIG. 13 shows the erasers of FIGS. 9a-9 c and 10 being wiped in adiagonal motion to provide an erasing surface that is between a thinerasing swath shown on FIG. 11 and the wide erasing swath shown on FIG.12 according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention is a graphic data-acquisition system which employs acontinuously active tracking system to provide a retrofittable apparatusfor converting a substantially planar surface into an electronic datacapture device. Various techniques are disclosed that allow thefabrication of a retrofittable assembly, such that any substantiallyplanar surface may be converted into an electronic data capture device.Thus, the components of the system are readily retrofittable, atrelatively low cost, to a wide variety of otherwise conventionalwriting-surface structures, such as so-called dry-erase whiteboards.

The invention employs any conventional triangulation technique to trackthe position and motion of a writer or eraser. As discussed above, manysuch techniques are known, but these techniques have traditionallyrequired a dedicated writing surface or have been otherwise unsuited forretrofit to an existing writing surface. The invention exploits toadvantage both the significant improvements in modern trackingtechnology and a novel and improved fitting technique that allows rapidand efficient retrofit of a tracking assembly to a dry-erase whiteboardor other planar surface, while providing a precision tracking systemthat accurately tracks a writing implement in three dimensions, thuscapturing all marks placed on the marking surface.

Further, by using an encoding facility associated with a writingimplement the invention provides the ability to distinguish whether thewriting implement is used for marking or as an erasing implement, aswell as determining the nature or character of written line width oreraser swath, for example specific color in the instance of a coloredwriting instrument. A data stream thus generated can be used in avariety of ways, such as for example, to feed information into thememory of a digital computer, and/or to feed information fortransmission to remote stations for live presentation of writingactivity occurring on the writing-surface area in the system.

FIG. 1 is an exploded perspective view of a retrofittable apparatus forconverting a substantially planar surface into an electronic datacapture device according to the invention. On FIG. 1, a writing surface14 is shown having a sensor array 10 attached thereto by an attachmentmethod 12. The writing surface may be any substantially planar surface,including for example a whiteboard or blackboard, a table, a videodisplay, a wall, a bulletin board, or a floor. The sensor array may beany conventional position sensing device, as is discussed above inconnection with the prior art, or as is more fully discussed below inconnection with MIR devices.

The attachment method may be any technique or device that affixes thesensor array to the writing surface. While this retrofittabilityarrangement may initially appear trivial, it is not, in light of thedifficulty of attaining accurate tracking of a marking implement tocapture position information that may be converted to a precisionrepresentation of text and drawings is not trivial. In this regard, theprior art has almost unanimously taught and relied on the use of adedicated, specialized writing surface to assure accurate positioning ofthe various sensors used to capture writing implement positionalinformation. This was necessary because the position sensing devicesrequired accurate calibration to detect minute variations in waveformsor light patterns. In such environment, both cumulative errors, andvibrations and movements attributable to motion of the writing surfaceduring repeated movement of a marker across the board surface tend toproduce unacceptable (and often unintelligible) results.

Thus, a key aspect of the invention involves the provision of a unitarysensor array that securely and rigidly fixes the relation between thevarious sensors within the array itself, such that the unitary arrayassembly may be repeatedly removed and affixed to any substantiallyplanar surface and yet still provide the high degree of precision andaccuracy necessary to effect a high quality capture of text anddrawings. This arrangement is particularly critical in a system thatemploys an active writing implement, where such implement producessignals having various patterns or frequencies which indicate differentfunctions, such as pen width or eraser operation, as well as differentcolors; and further where the act of marking upon the writing surfaceproduces vibrations and movement of the writing surface which may resultin inaccuracies due to variations in transmission times or movements inthe board surface.

FIG. 2 is a partially sectioned, side view of a unitary mobile sensorarray attachment method according to a first preferred embodiment of theinvention. In this embodiment of the invention the writing surface 14 issecured to a wall 22 using conventional methods. The sensor array 10 isaffixed to the writing surface using an attachment method 20 that maycomprise a double stick mounting tape or a temporary fastener, such asVelcro. This attachment method is particularly well suited for suchsurfaces as video displays, although it is also well suited for variousother applications.

FIG. 3 is a partially sectioned, side view of a mobile unitary sensorarray attachment method according to a second, equally preferredembodiment of the invention. In this embodiment of the invention, thesensor array 10 may be mounted to a wall 22 by a bracket 30. The bracketitself is secured to the wall with a fastener 32, such as a bolt ortoggle. The writing surface 14 may be secured to the wall by the samebracket, or it may be separately secured to the wall.

FIG. 4 is a partially sectioned, side view of a mobile unitary sensorarray attachment method according to a third, equally preferredembodiment of the invention. In this embodiment of the invention, thewriting surface 14 is secured to a wall 22 using conventionaltechniques. A bracket 42 having a portion that projects from the wall atan acute, upward angle, is secured to the wall by a fastener 44, such asa bolt or a toggle. The sensor array 10 is affixed to the bracket by asecond bracket 40 associated therewith that has a complementary channelthat is adapted to engage with the projecting portion of the wallmounted bracket in a secure fashion.

FIG. 5 is a partially sectioned, side view of a mobile unitary sensorarray attachment method according to a fourth, equally preferredembodiment of the invention. In this embodiment of the invention, thewriting surface 14 is secured to the wall 22 using conventionaltechniques. The sensor array 10 is affixed to a clip-on bracket 50 thatincludes a U-shaped portion 52 which is adapted to engage with an upperedge of the writing surface, for example with the upper edge of awhiteboard. This embodiment of the invention presumes that there is atleast of modicum of clearance between the wall and the writing surfaceto accommodate the U-shaped portion of the clip-on bracket.

FIG. 6 is a perspective view of a mobile unitary L-shaped sensor arrayaccording to the invention. In this embodiment of the invention, thesensor array is formed in an L-shaped configuration to allow threeintersecting sensor paths 61, 62, 63. Additional sensors 64, 65 may alsobe provided. This configuration provides a high degree of accuracy byallowing precise triangulation of writing implement position. Variouscomponents associated with the sensor assembly are positioned in amodule 66 that is mounted to the sensor array.

FIGS. 7a-7 c show alternative embodiments of the invention that provideside, bottom, and top mounting configurations for fitting a mobileunitary sensor array to a writing surface. FIG. 7a shows a writingsurface 14 having a sensor array 70 a affixed to a side thereof; FIG. 7bshows a writing surface 14 having a sensor array 70 b affixed to abottom thereof (and which may therefore also serve as a tray to holdvarious writing implements); and FIG. 7c shows a writing surface 14having a sensor array 70 c affixed to a top thereof.

It can be seen from FIGS. 2-7 that the invention provides a variety ofconfigurations that allow a mobile unitary sensor array to be fitted toany substantially planar writing surface. Thus, the sensor array may bemanufactured such that the individual sensors are all contained within astandard, unitary package and may be alternatively configured forattachment as shown in the figures by providing a variety of adaptersand/or fasteners. It is important to note that the accuracy of thesensor array is assured by calibrating the sensors during manufactureand within a common enclosure. Thus, the relationship of the sensors isdetermined during manufacture of the sensor array. As such, the sensorarray is readily retrofitted to any substantially planar surface by avariety of mechanisms with the assurance of a highly accurate andprecise determination of writing implement position. In this way, theinvention avoids the need for dedicated writing surfaces, provides atruly portable and compact electronic data capture device, and furtherprovides a data acquisition system that faithfully captures text anddrawings without the need for in situ calibration and recalibration.

Although the invention is calibrated at the factory, some users may wantthe option of calibrating the system in the field to further define andadd desired functionality. For example, the user may want to create a“dead” area on the planar surface, so that marks in this area are notforwarded to the computer. The user also may want to calibrate specificelements within the active area to create a toolbar, a video window, orother feature. In addition, user field calibration of the elementswithin the sensor array provides a wide range of user-definedconfigurations useful for portability or to work with varying sizes ofplanar areas. Calibration in the field may be achieved through a varietyof methods, including but not limited to the following:

(1) The system may instruct the user to tap the writing or erasinginstrument on the planar area at specific locations, such as upper rightand lower left, and calculate the active area from these coordinates.

(2) Alternatively, the user may place transmitters at specific locationswithin or on the boundaries of the active area. The sensor array woulddetect signals from these transmitters and calculate the active area ofthe planar surface.

Another feature of the invention is the provision of an active writingimplement. FIG. 8 is a partially sectioned, side view of a markingimplement according to the invention. While various multifunctionwriting implements have been identified above in connection with theprior art, such devices are somewhat limited in their ability to operatein connection with various tracking schemes. For example, someimplements are especially designed for optical schemes, while otherimplements are especially designed for electromagnetic tracking schemes.

The writing implement shown on FIG. 8 provides a sleeve 82 that has aninner diameter that is adapted to receive and securely retain a standarddry-erase marker 80. Thus, the herein-disclosed marking implement uses amarker that is familiar to the user and readily available. The sleeve istapered to follow the tapered contour of the pen and terminates with aswitch 90 that detects movement of the pen tip, i.e. when the tip of thepen is placed to the writing surface. Such detection generates a signalthat is communicated to the sensor array to indicate that the markingimplement is now in contact with the writing surface (and not above thewriting surface, as such detection would provide a false plane ofinformation to the sensor array). Thus, the sensor array only tracksmarking implement position when the marking implement is registered tothe writing surface. Such signal may also communicate actual positionalinformation, for example by providing a relay or feedback of trackinginformation received at the pen, such that a time-based markingimplement position may be derived.

Such signal may also be modulated or digitally coded to identify aparticular marking implement function or color, for example whether themarking implement is a red or blue pen, whether the marking implement isdrawing a thin line or a thick line, or whether the marking implement isan eraser. In connection with this last point, the marking implementherein disclosed includes a collar 84 that is adapted to be securelyfitted to the sleeve 82. The collar activates a switch 85 that indicatesit is fitted to the sleeve. A plunger 86 is movable fitted within thecollar. An eraser 88 is securely received within the plunger.

In operation, the eraser is pressed to the writing surface to erasemarking thereon. This action pushes the plunger into the collar, therebyactivating the switch 90, and thereby indicating contact of the eraserwith the writing surface. The presence of the collar operates the switch85, thereby indicating that the marking implement is performing aneraser function.

In existing electronic copyboard systems that send eraser data to acomputer, the eraser has a predefined size. Systems assume that the userhas erased an area at least equal to the total area of the bottom of theeraser. Thus, to erase a smaller area, the user must locate and use asmaller eraser. If the user attempts to erase a small area with only theside of the eraser, which is the natural method most users wouldattempt, systems receive inaccurate data regarding the size of the areathat has been erased. The two-point eraser disclosed herein solves thisproblem by providing users with the capability to erase a wide range ofareas with a single tool.

The two-point eraser 110 (FIGS. 9a-9 c) consists of a rectangular orround thin shape handle 100, a thin erasing edge 102, and twotransmitters 103, 104. One transmitter is attached to each end of theerasing edge, as shown in FIG. 10. To erase a thin area, the user wipesthe eraser on the board 112 in a motion that is parallel to the Y axisof the eraser (FIG. 11). To erase a wide area, the user wipes the eraserin a motion that is parallel to the X axis (FIG. 12). The eraser alsocan be wiped in a diagonal motion to achieve any size between “thin” and“wide” (FIG. 13). Thus, the invention provides an eraser that isergonomically designed to operate in a similar fashion to that of astandard blackboard/white-board eraser, in which the user can rapidlydraw the eraser back and forth across the marking surface to erase alarge portion of the marking suface, if desired, and in which the usercan precisely control the moment and profile of the eraser to eras onlyspecific portions of the marking surface. Accordingly, theherein-described_accurately locates the ends of the eraser by use of thetwo transmitters, and thus defines a continuously variable and easilycontroled eraser swath.

With regard to the actual determination of the position of the markingimplement, the invention is readily adapted for use with any modernlocating technique, including any of those techniques discussed above inconnection with the prior art. The presently preferred embodiment of theinvention operates in connection with a triangulation scheme thatincludes a Micropower Impulse Radar (MIR) device. The MIR device is apulsed radar similar to other ultra-wideband radars, but it emits muchshorter pulses than most radars and, because it is built out of a smallnumber of common electronic components, it is compact and inexpensive.MIR devices are used in such applications as automobile back-up systemsand in hand-held tools for finding studs and other objects behind walls.

One feature of MIR devices is the pulse generation circuitry. Each pulseis less than a billionth of a second and each MIR device emits about twomillion of these pulses per second. Actual pulse repetition rates arecoded with random noise to reduce the possibility of interference fromother radars, while each MIR device is tuned to itself. The same pulseis used for transmitting to send via the transmit as for sampling thereceived signal. Three direct advantages of the short pulse-width are:

The MIR operates across a wider band of frequencies than a conventionalradar, giving high resolution and accuracy, but also making it lesssusceptible to interference from other radars.

There are extremely low power requirements because current is only drawnduring the short pulse time and the pulses are infrequent. For example,one type of MIR unit can operate for years on a single AA battery.

The microwaves emitted by the pulse are at exceedingly low, andtherefore safe, levels (microwatts). In fact, the MIR emits less thanone-millionth the energy of a cellular telephone.

As with conventional radars, the antenna configuration on MIR devicesdetermines much of its operating characteristics. Several antennasystems have been designed to match the ultra-wide frequencycharacteristics of the MIR sensor. For the standard MIR motion sensorwith a center frequency of about 2 GHz, a small 1.5-inch antenna may beused. However, the MIR device is also flexible enough that it canoperate at a relatively lower center frequency, using larger antennasystems, giving it longer range.

Averaging of many thousands of pulses is done on the MIR device toreduce the effects of noise and to increase sensitivity. A singlereceived pulse in the nanosecond time scale may be contaminated withvarious forms of outside interference, but if the returns of many pulsesat the same range gate are combined, the result is much morerepresentative of the actual return. The number of averages per rangegate is adjustable (nominally it is about 10,000 samples).

The exact pulse emission and detection times are randomized for at leastthe following reasons:

Continuous wave (CW) interference, such as from radio and TV stationharmonics, may cause beat frequencies with the received echoes that cantrigger false alarms. When the 10,000 samples of MIR return echoes areaveraged at randomly-dithered times, random samples of CW interferenceare effectively averaged to zero.

Random operation also means that multiple MIR units can be collocatedwithout interfering with each other. Channel allocations are not neededand a nearly unlimited number of sensors can be in the same vicinityeven though they occupy the same wideband spectrum. This is particularlyuseful in a whiteboard-type application, where a plurality of sensorsare used to triangulate marking implement position.

Although the invention is described herein with reference to thepreferred embodiment, one skilled in the art will readily appreciatethat other applications may be substituted for those set forth hereinwithout departing from the spirit and scope of the present invention.Accordingly, the invention should only be limited by the Claims includedbelow.

What is claimed is:
 1. A retrofittable apparatus for converting asubstantially planar surface into a writing surface for an electronicdata capture device, the apparatus comprising: a unitary sensor arraythat securely and rigidly fixes a relation between a plurality ofsensors and that provides a tracking function to determine the positionof a marking implement on the writing surface; and a means for removablycoupling the unitary sensor array to the substantially planar surface.2. The apparatus of claim 1, wherein said substantially planar surfaceis any of a whiteboard, a blackboard, a table, a video display, a wall,a bulletin board, and a floor.
 3. A retrofittable apparatus forconverting a substantially planar surface into a writing surface for anelectronic data capture device, the apparatus comprising: a unitarysensor array that provides a tracking function to determine the positionof a marking implement on the writing surface, an active area on theplanar surface; and a means for removably coupling the unitary sensorarray to the substantially planar surface.
 4. The apparatus of claim 3,wherein the active area comprises any of a toolbar, video window, andother feature.